CVE-2026-38639 Overview
CVE-2026-38639 is a denial-of-service vulnerability in the parse_month function located in /time/strptime.rs of relibc, the C standard library implementation for the Redox operating system. The flaw exists in commit ab6a2e and allows a remote attacker to crash affected applications by supplying a crafted input to the strptime parser. The issue is categorized under [CWE-20] (Improper Input Validation).
Critical Impact
Attackers can trigger a denial of service in any application that uses relibc's strptime implementation to parse untrusted date strings, disrupting availability of affected services.
Affected Products
- relibc (Redox OS C standard library) at commit ab6a2e
- Applications linking against the vulnerable relibc build
- Redox OS components depending on strptime for time parsing
Discovery Timeline
- 2026-06-26 - CVE-2026-38639 published to NVD
- 2026-06-29 - Last updated in NVD database
Technical Details for CVE-2026-38639
Vulnerability Analysis
The vulnerability resides in the parse_month helper of relibc's strptime implementation in /time/strptime.rs. The function converts textual month representations into numeric values when parsing formatted date strings. Improper validation of the parser's input state permits a crafted string to drive the function into an unrecoverable condition, terminating the process.
Because strptime is commonly exposed to externally sourced date data such as HTTP headers, log entries, and file metadata, the attack surface extends to any network-facing application built against the affected relibc commit. The impact is limited to availability. Confidentiality and integrity are not affected according to the published CVSS vector.
Root Cause
The defect stems from improper input validation ([CWE-20]) inside parse_month. The routine does not correctly handle malformed or unexpected month tokens supplied through the format-driven parser, leading to a fatal runtime error rather than a graceful parse failure and error return.
Attack Vector
Exploitation requires no authentication and no user interaction. An attacker submits a crafted input string that reaches strptime in a vulnerable process. Any input path that forwards untrusted data to date parsing routines — for example, request headers, log ingestion, or file format parsers — is a viable channel. The proof-of-concept published in the GitHub PoC Repository demonstrates the crash condition against the affected commit.
No verified exploitation code is included here. Refer to the Redox Issue Tracker for technical details of the reproducer.
Detection Methods for CVE-2026-38639
Indicators of Compromise
- Unexpected termination or panic of processes that invoke strptime shortly after receiving external input
- Crash traces referencing parse_month or /time/strptime.rs in relibc
- Repeated malformed date strings observed in application logs prior to service restarts
Detection Strategies
- Monitor for abnormal exit codes and restart loops in services linked against relibc at commit ab6a2e
- Inspect application logs for parser errors preceded by non-standard month tokens or truncated date fields
- Correlate crash events with inbound requests carrying user-controlled date or timestamp values
Monitoring Recommendations
- Enable core dump collection on services using relibc to capture faulting stack traces
- Alert on elevated process crash rates for Redox OS workloads and applications built with relibc
- Track inbound traffic patterns that deliver malformed date fields to affected endpoints
How to Mitigate CVE-2026-38639
Immediate Actions Required
- Identify all binaries and services built against relibc commit ab6a2e or earlier vulnerable revisions
- Rebuild affected applications against a patched relibc revision from the upstream repository
- Validate and sanitize date strings at the application layer before passing them to strptime
Patch Information
A fix has been proposed and tracked upstream. Review the Redox Merge Request for the code change addressing the parse_month input handling, and the Redox Work Item for status. Rebuild and redeploy dependent binaries after applying the update.
Workarounds
- Reject or pre-validate untrusted date inputs using an application-level parser before invoking strptime
- Isolate services that must parse untrusted date data behind supervisor processes that restart on crash
- Restrict exposure of components using vulnerable relibc builds to trusted network segments until patched
# Configuration example - identify binaries linked against relibc
ldd /path/to/binary | grep -i relibc
# Rebuild against patched relibc
git -C relibc fetch origin
git -C relibc checkout <patched-commit>
cargo build --release
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
